Which two statements about BGP facilitate the prevention of routing loops between two autonomous systems? (Choose two.)

1. A. EBGP routers will append their AS number when advertising routes to their neighbors.
2. B. EBGP routers will only accept routes that contain their own AS number in the AS_PATH.
3. C. EBGP routers will drop routes that contain their own AS number in the AS_PATH
4. D. EBGP routers will prepend their AS number when advertising routes to their neighbors

Correct Answer: AC
BGP (Border Gateway Protocol) is a protocol designed to exchange routing and reachability information among autonomous systems (AS) on the internet1.
✑ Option A is correct. When an EBGP router advertises routes to its neighbors, it appends its AS number to the AS_PATH attribute1. This is a key mechanism in BGP to prevent routing loops1.
✑ Option C is correct. BGP has a built-in loop prevention mechanism whereby if a BGP router detects its own AS in the AS_PATH attribute, it will drop the prefix and will not continue to advertise it2. This helps to prevent routing loops2.
✑ Option B is incorrect. EBGP routers do not accept routes that contain their own AS number in the AS_PATH2. Instead, they drop such routes as part of the loop prevention mechanism2.
✑ Option D is incorrect. While it??s true that EBGP routers append their AS number
when advertising routes, they do not prepend their AS number1. The term ??prepend?? in BGP usually refers to a technique used to influence path selection by artificially lengthening the AS_PATH3.